1. Field of the Invention
The present invention relates to an abnormality determination apparatus and method for a blow-by gas feedback device for feeding a blow-by gas to an intake system of an internal combustion engine through a blow-by gas passage connected to the intake system, and an engine control unit.
2. Description of the Prior Art
Conventionally, as this type of abnormality determination apparatus for a blow-by gas feedback device, one described, for example, in Laid-open Japanese Patent Application No. 10-184335 is known. In Laid-open Japanese Patent Application No. 10-184335, a throttle valve is provided in an intake pipe of an internal combustion engine, and a bypass passage is connected to the intake pile for bypassing the throttle valve. An ISC valve is provided in the bypass passage to control the rotational speed of the internal combustion engine to a target rotational speed during an idle operation of the engine by controlling the amount of intake air. A blow-by gas passage is connected to the intake pipe at a location downstream of the throttle vale. This abnormality determination apparatus detects the opening of the ISC valve during the idle operation, and determines that the blow-by gas feedback device is abnormal by some cause such as the blow-by gas passage coming off the intake pipe, a damage, or the like, when the detected opening is smaller than a predetermined determination value.
Abnormalities of the blow-by gas feedback device are determined in this way for the reason set forth below. Specifically, when the blow-by gas passage comes off or is damaged, air flows into the intake pipe from such a location, so that the amount of intake air correspondingly increases, resulting in a rise in the rotational speed of the internal combustion engine beyond the target rotational speed. Associatively, the opening of the ISC valve is controlled to a smaller value than that during a normal operation for reducing the intake air amount in order for the increased rotational speed to converge to the target rotational speed. As a result, the opening is smaller than the determination value.
However, when the conventional abnormality determination apparatus described above is applied to a blow-by gas feedback device which has a blow-by gas passage connected to an intake pipe at a location upstream of a throttle valve, even if the blow-by gas passage comes off or is damaged, causing air to flow in from such a location, the opening of the ISC valve is controlled including the amount of the inflow air. As a result, the opening of the ISC valve is controlled in the same manner irrespective of whether the blow-by gas feedback device is abnormal or normal, so that abnormalities of the blow-by gas feedback apparatus cannot be appropriately determined based on the opening of the ISC valve.